This invention relates to a communication system for transferring desired stream data, and more particularly to a communication system and a communication path control method for transferring stream data such as video data from a transmission node to a reception node in a network.
The entire contents of Japanese Patent Application No. 8-243560 filed on Sep. 13, 1996 are incorporated herein by reference.
Recently, as the computer network technology and the communication technique of digital information are developed, a system for transferring a string of data items (which is hereinafter referred to as stream data) constructed on the time series to realize "video on demand", for example, is developed.
In the above system, for example, a requested video signal such as a moving picture is sequentially converted into digital information (picture frames). Further, the digital information is transferred as stream data from a transmission node which is a source node (video server or the like) to a reception node which is a destination node (user terminal, client or the like) via a communication path on the network. At this time, the transfer rate of the stream data is determined dependent on the reception speed of the reception node side.
Therefore, in the process of transferring continuous data such as stream data, the transmission node side cannot effect the sequential process of transferring batches of requested stream data at a high transfer rate and then effecting the stream data transferring process in response to a next request. That is, the transmission node side cannot be released until the stream data transferring process is completed.
As a system for solving the above problem, there is provided a system for providing a relay node on a communication system for transferring stream data and temporarily buffering stream data transferred from the transmission node into a buffer memory by use of the relay node. With the above system, the transmission node can transfer batches of stream data at a high transfer rate irrespective of the reception speed of the reception node. The relay node buffers stream data transferred from the transmission node and then transfers the same to the reception node side at a transfer rate corresponding to the reception processing speed.
A plurality of relay nodes can be provided between communication nodes (transmission node, reception node) for transferring stream data. When communication is made between communication nodes connected to the network, it is possible to set a stream transfer path including some other communication nodes connected to the network as relay nodes according to a control instruction from a control node.
While the stream data is being transferred via a plurality of communication nodes, a server or the control node which is previously determined in the communication system is required to acquire the state of each communication node and set operation parameters in order to change the stream transfer path to an adequate stream transfer path.
As the applicable technique for acquiring the state of each communication node and setting the operation parameters, a method for directly controlling each communication node by use of an SNMP (Simple Network Management Protocol) which is a management protocol of Internet standard from the control node, and a method which is similar to the above method and uses a CMIP (Common Management Information Protocol) which is a management protocol of OSI (Open System Interface) standard permitting the hierarchical structure on the control node side are known.
In the conventional communication system, transfer of stream data flowing via a plurality of communication nodes on the network is managed and controlled by the control node using a management protocol such as SNMP, CMIP.
The conventional management protocol such as SNMP, CMIP is designed for the purpose of controlling a network device and generally constructed to effect the management operation for part of or whole portion of the hardware device and a management information model representing the structure of a to-be-managed object is generally represented by a static description. Further, use of the conventional management protocol is permitted only for operators having the privilege of managing the network.
Therefore, in the conventional communication system, since the control node effects the transfer control and management of stream data according to the management protocol described before, a communication node itself (or application associated with the communication node) for effecting data transfer cannot manage or control the transfer of individual stream data items transferred on the network according to the application form of the stream data. Therefore, fixing of the transfer control and management imposes restrictions on the operation of transferring stream data via a plurality of communication nodes on the network.
In a case where a communication node itself for transferring data manages and controls the transfer of stream data, stream transfer on the network occurs between any communication nodes, the communication node is frequently set or released and a large number of streams simultaneously flow on the same communication node.
Therefore, in order to manage and control the transfer of stream data, the parameter control process and acquisition of the state of stream transfer between terminal nodes (communication nodes) on the network are required. However, since the conventional management protocol is designed for the purpose of control of the network device, the management protocol is insufficient in function.
Further, in a case where the communication node itself effects the management and control of stream data transfer, the transfer of stream data is effected by use of an application associated with the communication node and accesses from a plurality of user applications relating to the stream transfer may occur, and therefore, a plurality of unspecified communication nodes will acquire the state of stream transfer and effect the parameter control. As a result, if the process of managing and controlling desired stream transfer is permitted simply by use of the conventional management protocol in each communication node, a problem occurs in the security management of stream data.
Further, in the conventional communication system, in a case where a control message cannot be directly transferred from the control node to each communication node, it is necessary to use some communication nodes as relay nodes for control communication. Memory resources on the communication nodes are consumed by the overhead for managing the connection structure and this may impose a restriction on the maximum number of streams which one communication node can process.